# Voltage regulator - must have for electrical system?

Discussion in 'Instruments / Avionics / Electrical System' started by Battson, May 11, 2012.

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1. May 11, 2012

### Battson

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As the total planned cost of my build climbs past another milestone, I am trying to plan all the surprisingly expensive little odds and ends that I'll need to buy (which all add up, thousands at a time!).

Does having an alternator-driven electrical system, feeding a battery which provides 12VDC power to all the (very expensive) EFIS, EMS, COM, etc systems; require a voltage regulator to prevent damage to equipment?
Or is keeping the avionics bus "off" during start and shutdown enough to mitigate the risk........?

Thanks to any electrical types who are able to help!

2. May 11, 2012

### TFF

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Without a regulator it will probably burn its self up trying to supply its max power. You would have to hardwire the field but then it will only charge flat out. Regulators are cheap.

3. May 11, 2012

### Dana

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You have to have a regulator. A regulator is an integral part of an electrical system with an alternator; it controls the field current in the alternator so it outputs the correct voltage. Without it, the alternator would produce up to 40V or so; it'd blow up the battery as well as the avionics. Many modern automotive alternators have a solid state regulator built in.

-Dana

And they shall beat their swords into plowshares, for if you hit a man with a plowshare, he'll know he's been hit!

4. May 11, 2012

### SVSUSteve

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There's a reason why I've strongly considered paying Ron Wantajaa off to design the electrical layout for my aircraft (or at least correct the glaring errors in my own electrical "engineering"). It's too **** confusing in all but the simplest designs.

5. May 11, 2012

### Dan Thomas

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An alternator can easily produce 150 volts. Back in the '70s there was a doodad you could buy to install in your car or truck that had a switch, a neon indicator light, and a 110 volt receptacle all installed in a neat plastic box for something like $75 at the time. The output was DC, not AC, so only lights and series-wound motors could be operated, but I bought one and it was handy. Wondering what was in it, I drilled out the rivets holding it shut and discovered inside nothing more than the backsides of the DPDT switch, neon bulb, and receptacle, and a resistor. Could have bought it all for about$7. All the switch did was take the regulator out of the field circuit and connect the field directly to the battery, and disconnect the battery from the alternator's output. You had to have some way of locking the throttle. You ran the RPM up until the neon bulb lit ( the resistor raised the bulb's nominal ignition voltage from 86 to 110) and locked the throttle there. Every ten or 15 minutes or so you'd switch back to recharge the battery, since it was not being charged while in the 110V mode and the field was drawing it down at 4 amps or so.
If one was to run the RPM higher, the voltage kept rising. The only risk is to the diodes in the alternator, since they might only be 50 PIV in some units. The alternator is capable of 60 amps or thereabouts, which means it'll produce 6600 watts at 110 volts without getting overheated.

Yes, the regulator is very important.

Dan

6. May 11, 2012

### Joe Fisher

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7. May 11, 2012

### Battson

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Ok - good to know - and these don't typically come with a Lycoming engine / alternator I presume? Goodbye another $130, but I dont mind. It's less than 0.1% of the total cost anyway!! :speechles I feel woefully inadequate when it comes to installing my (comparatively simple) electrical system. I am sure something, will at some point, catch fire during the test run. :ban: Is there a standard way of learning what's required? I only learned about this component by pure chance here... 8. May 11, 2012 ### fly2kads ### fly2kads #### Well-Known MemberHBA Supporter Joined: Jan 2, 2010 Messages: 1,443 Likes Received: 526 Location: Justin, TX 9. May 11, 2012 ### Battson ### Battson #### Well-Known Member Joined: Jan 30, 2012 Messages: 610 Likes Received: 96 Location: New Zealand I am still reading my way through AC43-13, started about 4 months back..... :grin: How about an alternator filter - are they optional or required for modern COM / glass panel applications? 10. May 11, 2012 ### berridos ### berridos #### Well-Known Member Joined: Oct 10, 2009 Messages: 804 Likes Received: 47 Location: madrid Excellent link. Thanks for sharing 11. May 11, 2012 ### TFF ### TFF #### Well-Known Member Joined: Apr 28, 2010 Messages: 11,421 Likes Received: 3,167 Location: Memphis, TN They are optional but more than likely you will need one. 12. May 11, 2012 ### Joe Fisher ### Joe Fisher #### Well-Known Member Joined: Feb 11, 2007 Messages: 1,378 Likes Received: 374 Location: Galesburg, KS South east Kansas 13. May 12, 2012 ### Dan Thomas ### Dan Thomas #### Well-Known Member Joined: Sep 18, 2008 Messages: 4,785 Likes Received: 2,015 You can buy a generic auto regulator for a lot less than$130. You could even go to the junkyard and get one from a 1980s or older car or truck for next to nothing. For a few years before they went to integral regulators, the firewall-mounted units were electronic and worked well.

Alternator noise filters, as found on the typical lightplane, have both an inductor and a capacitor in them. All the current flows through the inductor, which resists rises and falls in current flow (which dampens the little waveforms) and the capacitor bleeds off to ground more of those waveforms.

Dan

14. May 15, 2012

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